When performing image guided surgery using tracking devices, the fields set up by these tracking devices may be affected through the interaction of metal and other conductors with position sensors (hereinafter “position indicating elements”) associated with the tracking devices. This is because conductors alter the way in which these fields are produced, causing field lines to bend and otherwise influence the way in which the field generator of the tracking device sets up a field in a “measurement volume.” In general, the conductive material, the shape of the conductive material, as well as the orientation and location of the conductive material relative to the field generator and detector, are all important in assessing the interaction of the conductive material with a tracking device such as, for example, a magnetic tracking device.
In addition to distortions caused by metal objects and conductors, stray fields introduced by electrical or electromagnetic devices may also alter the measurement field of a tracking device. All of these factors may result in an alteration of the accuracy with which the tracking device reports position and orientation information regarding its associated position indicating elements.
Furthermore, tracking devices and their associated field generators may undergo various forms of damage over their lifetime that may affect their accuracy. Damage may occur, for example, from mechanical sources such as impacts, electrical sources such as high voltages, and/or magnetic sources such as high ambient magnetic fields. Normal aging of components may also affect the accuracy of a tracking device.
Suppliers of tracking equipment have adopted a variety of techniques to mitigate the effects described above and to ensure the fields produced by their systems are uniform and accurate. However, these techniques are not always adequate or sufficient. For example, these methods may be complicated and time consuming or may require specialized equipment. They may also not be appropriate to assess the particular operating environment that the tracking equipment may be used in. These and other problems exist.